The present invention relates generally to barbecue grills and more particularly to an electronically controlled barbecue grill employing a microprocessor-based electronic circuit for monitoring fuel status, cooking time and temperature and for monitoring and controlling electronic ignition. The electronic circuit includes a human-readable display and comprises a compact and fully integrated, battery-powered control package which affords great convenience and high reliability.
One popular style of conventional barbecue grill in use today employs a containment casting with a gas burner assembly disposed therein and supplied with fuel stored under pressure in a replaceable or refillable canister. Typically, a manually adjustable fuel supply valve is interposed between canister and burner to allow the user to adjust the height of the flame and the cooking temperature. Normally a mating lid is hingedly attached to the casting for use in covering the grill cooking surface and for defining an oven space beneath the lid and within the casting. Some barbecue grills of this type have an analog thermometer of the bimetal type attached to the lid to allow the user to determine the temperature within the oven space, when the lid is closed. In addition, some models may include a push-button operated electronic ignition. In use, the user adjusts the gas valve to establish fuel flow into the burner and then depresses the electronic ignition button, causing a momentary spark to ignite the fuel at the burner.
The present invention affords a great deal of convenience not found in conventional barbecue grills. The invention employs a microprocessor-based electronic circuit which monitors and controls various functions of the grill.
A canister weighing system with electronic output provides the data used by the microprocessor to determine the quantity of fuel remaining. The microprocessor displays the quantity of fuel remaining either as a numerical fractional value, or in terms of remaining burning time, based on a calculation performed by the microprocessor. The electronic circuit also includes means for user input of a desired cooking time. The microprocessor circuit includes a real time clock for comparison with the desired cooking time to provide an alarm when the desired cooking time has elapsed. In addition, the desired cooking time is compared by the microprocessor with the remaining burning time for the fuel within the canister. If the microprocessor determines that the fuel remaining in the canister is insufficient to complete the desired cooking time, a notification of the low fuel condition is automatically displayed when the desired cooking time is first entered. This provides the user ample opportunity to fill or replace the fuel canister before beginning to cook. The microprocessor also automatically warns of a low fuel condition when the quantity of fuel drops below 1/8 of the full level.
The electronic circuit also includes an automatic electronic ignition control which may be initially activated by the user, simply by turning the gas supply valve to its fully on position. A first ignition event occurs in response to manual actuation, causing the electronic ignition device to be actuated. An electronic flame sensing device monitors whether a flame is produced in response to the ignition event. If a flame is not present after the first ignition event, the electronic circuit automatically causes one or more subsequent ignition events to occur, without further human interaction, in an effort to ignite the burner. After a predetermined number of attempts at ignition, if no flame is produced, an error message is displayed and an audible alarm is sounded to allow the user to correct the problem or attempt to light the burner manually with a match.
The same flame sensing apparatus continues to monitor the flame even after ignition and the electronic circuit automatically initiates a reignition cycle if the flame is extinguished. This might occur, for example, if a strong wind were to blow out the flame.
Anytime the electronic circuit is unable to ignite or reignite the flame after a predetermined number of tries an error message is displayed, giving the most likely cause of the problem, the principal reasons being inadequate fuel or insufficient battery energy to cause an ignition spark. Accordingly, the control circuit monitors fuel level and battery voltage to provide the appropriate "Fuel Out" and "Low Battery" messages.
The electronic control circuit also employs a thermistor sensor attached to the mid-rear portion of the lower containment casting. The thermistor provides an electrical signal indicative of the cooking temperature. The microprocessor-based control circuit can display the temperature on the integral display device located on the front console. This same display device is also used to display the fuel status messages, electronic timer messages and error messages, when appropriate.
In one user-selected mode the microprocessor cycles various information onto the display device in a rotating sequence. In this fashion, fuel level, fuel time, cooking temperature and cooking time are sequentially displayed.
For a more complete understanding of the invention, its objects and advantages, reference may be had to the following specification and to the accompanying drawings.